1. Field of the Invention
The present invention relates to a method of measuring and regulating the pressure in an inflatable sealing cuff of a tracheal tube introduced into the trachea of a patient, in particular, for generating a constant contact pressure of the sealing cuff against the trachea for the purpose of producing gas-tight respiration for the patient and avoiding the aspiration of fluids from the patient's oral cavity into his breathing passages, and to an apparatus for implementing the method.
2. Background Information
It is known to employ endotracheal tubes equipped with a cuff that is inflated within the trachea in order to aid the breathing of intensive care patients. The cuff performs two significant functions: it permits gas-tight respiration, and it avoids the aspiration of fluids from the patient's oral cavity into his breathing passages. A fixed cuff pressure of about 20 mbar is usually selected to meet these requirements.
FIG. 1 depicts a cuff arrangement as disclosed in DE-GBM (German Utility Model Patent) 91/04,637 for sealing a cuff 12 on a tube 10 which is inserted into the trachea of a patient. The arrangement includes a compressed air reservoir 14 fed with compressed air from a compressed air source (not shown) by way of a reducing valve 26, a pressure conduit 16 leading from compressed air reservoir 14 to cuff 12, an electrically actuatable air intake valve 18, an electrically actuatable air discharge valve 20, a pressure sensor 22 for measuring the pressure in cuff 12, and a control unit 24. Reducing valve 26 is set to a pressure value that lies clearly above a sealing-pressure of about 20 mbar, but below a pressure which could lead to tearing of the cuff. Control unit 24 measures the actual pressure in cuff 10 with pressure sensor 22 and compares the actual measured pressure with a calculated desired pressure. If the actual measured pressure is determined to be too low, control unit 24 actuates air intake valve 18, so that the pressure in cuff 10 is increased by connection with compressed air reservoir 14. If, however, the actual measured pressure exceeds the desired pressure, air discharge valve 20 is actuated, cuff 12 is thereby connected with the ambient air, and the pressure in the cuff is reduced correspondingly.
However, if there is a great and steep increase in pressure caused, for example, by coughing of the patient, the control unit 24 is not able to respond appropriately.